Topic: Ionic bonds - formation and types

Target group

Elementary school student (grades 7. and 8.)

Core curriculum

Elementary school. Chemistry.

II. Internal structure of matter. Pupil:

9) describes the function of the electrons of the outer shell in the joining of atoms; uses the concept of electronegativity to determine the type of bonds (covalent, ionic) in given substances;
11) uses the concept of an ion (cation and anion) and describes how the ions are formed; determines the charge of metal ions (e.g. Na, Mg, Al) and non‑metals (e.g., O, Cl, S); describes the formation of ionic (e.g., NaCl, MgO).

General aim of education

The student explains the essence of the formation of ions from atoms

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to explain the concepts of ion, cation and anion;

• to explain the mechanism of ion formation on the examples: Na, Mg, Al, Cl, S;

• to write the ionic configuration of the ions on the examples: Na, Mg, Al, Cl, S;

• to explain the role of valence electrons in the formation of ions.

Methods/techniques

• activating

  • discussion;

  • snowball method.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards;

• periodic table of elements.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

Realization

1. The teacher asks students to remind them about the mechanism of unpolarised and polarized covariance formation. Willing/selected students provide answers, the other students and the teacher complement them if necessary.

2. The teacher explains the concept of electronegativity. Using the periodic table of elements, he explains which elements have the smallest and which are the most electronegative. Indicates how the type of chemical bond is determined based on electronegativity.

3. The teacher displays on the multimedia board the „The diagram of an ion formation from an atom” from the abstract. He asks students to explain in their own words what the process is about and define the concept of ion. Informs that students will work on the snowball method. First, they work on the pairs in the pairs. Then they join the fours, compare their studies, verify them and establish a common position. In the next steps, the students join in more numerous groups and follow the previous pattern until a common definition is created. If necessary, the teacher completes the information.

4. The lecturer, displaying the „Types of Ions” scheme from the abstract on the multimedia board. He asks students to count up to 2. He informs that the task of „numbers 1” is to prepare information, when a cation and atoms are formed of which elements they create, and the task of „numbers 2” – when the anions and atoms of which these elements are formed. Students do the job. Then the teacher asks students to share knowledge with each other. After exchanging information, the teacher randomly selects several „numbers 1” and asks for the information provided by the „numbers 2” and vice versa. If necessary, give explanations.

5. The teacher asks for the „numbers 1” and „numbers 2” to form groups. The task of „numbers 1” is to develop the question „How does sodium ion arise?” and the task of „numbers 2” – „How does the chlorine ion arise?”. The teacher asks that the students, while preparing their studies, pay attention to the rays of atoms and ions (cations / anions). After the expiration of the appointed time, group representatives discuss issues using abstract schemes.

6. The lecturer displays on the multimedia board the presentation „Ions formation”. The students explain the equations presented on the boards, and write their observations in the form in the abstract.

7. The teacher explains to students on the example of magnesium and aluminum ions, what load values ion can have. Saves the electronic configuration for the atom and for the ion.

8. At the end of the lesson, the teacher asks students to do interactive exercises – individual activity.

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Imagine that you have the opportunity to interview an academic - a specialist in the field of today's lesson. What questions would you like to ask him? Write them down.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Ionic bonds - formation and types

Most of the chemical elements do not occur in nature in the free state, but form chemical compounds with other elements. Only few simple substances exist in the form of individual atoms. These include noble gases, i.e. chemical elements belonging to the 18th group of the periodic table (helium). Their relatively stable electron configuration is a model for other elements. During the formation of typical chemical bonds atoms of the elements strive to obtain an electron configuration of the closest noble gas in the periodic system. This is done in a variety of ways. Elemental atoms can share electrons. They can also give them to other atoms of the elements or take them from atoms. As a result of these processes, ions arise from atoms.

Ions with a positive charge are called cations, while those with a negative charge – anions. The sodium ion, which was created by electron donation of sodium atom, is a cation. In turn, the chlorine atom, which accepted the electron, becomes an anion.

Atoms of metals (especially those belonging to the 1st and 2nd group of the periodic table) form cations. The atoms of some nonmetals may form anions as a result of electrons acceptation.

As a result of the electron transfer from the sodium atom, an ion is formed. As you remember, in every atom the positive charge of the nucleus is equal to the negative charge of the electron cloud (the number of protons is equal to the number of electrons) and the atom is electrically neutral. Note that in the sodium ion the number of protons and electrons are not identical: there are 11 protons in the atomic nucleus and 10 electrons in the space around the nucleus. Thus, 1 proton is not „balanced” by the electron. Therefore, the whole ion has a charge of a proton (equal to the elementary positive charge). The sodium ion is said to be positive. This ion is described by the „+” sign next to the symbol of the chemical element: ${\mathrm{Na}}^{+}$.

The diagram below shows the changes in the electron configuration of the sodium atom during the formation of the ion.

The mechanism of formation of a positive sodium ion can be written using the Lewis structures or only the symbol of the chemical element:

$\text{Na·}\stackrel{\text{ electron donation }}{\to }{\text{Na}}^{\text{+}}$

$\text{Na}\stackrel{}{\to }{\text{Na}}^{\text{+}}\text{+ }{\text{e}}^{-}$

The process of sodium ion formation can also be presented using the electron configurations of the atom and its ion:

$\text{Na [2, 8, 1] }\stackrel{\text{electron donation}}{\to }{\text{Na}}^{\text{+}}\text{[2, 8]}$

The sodium atom has 11 electrons. One of them is placed on the last shell. After its release, the sodium atom has 10 electrons and an electron configuration of the noble gas closest it in the periodic table – neon. Thanks to this, he gains a permanent configuration.

As a result of the electron being accepted by the chlorine atom, an ion is formed. Due to the presence of an additional electron, this ion is charged with a negative charge (equal to the elementary negative charge). This ion is described by the “–” sign next to the symbol of the chemical element: ${\text{Cl}}^{-}$

The process of this ion formation can be described by the equations:

$\text{Cl }\stackrel{\text{electron accepting}}{\to }{\text{ Cl}}^{-}$

$\text{Cl + }{\text{e}}^{-}\text{ → }{\text{Cl}}^{-}$

$\text{Cl [2, 8, 7] }\stackrel{\text{electron accepting}}{\to }{\text{ Cl}}^{-}\text{[2, 8, 8]}$

The diagram below shows the changes in the electron configuration of the chlorine atom during the formation of the ion.

As you remember, the chlorine atom in the molecules ${\text{Cl}}_{\text{2}}$ or $\text{HCl}$, to achieve an stable electron configuration, shares a single electron with a different atom. However, in the presence of a sodium atom, it behaves differently - it receives an electron from it to its outer shell. The number of its electrons is then increased by 1 and the atom gains the electron configuration proper to argon, which in the periodic table is located just after the chlorine.

Atoms can donate and accept more than 1 electron.

In the magnesium atom ($\text{Z=12}$) there are 12 protons and the same number of electrons. When interacting with other atoms, the atom $\text{Mg}$ can „get rid of” 2 electrons forming its external electron shell. In the formed ion the number of electrons decreases and there is an excess of positive charges (12 p) in relation to the negative ones (10${\text{e}}^{-}$). Therefore, the magnesium ion is a cation and its charge is equal to two elementary positive charges. Such cations are said to be dications and are recorded as follows:${\text{Mg}}^{\text{2+}}$.

The process of magnesium ions formation can be described by the equation:

$\text{Mg → }{\text{Mg}}^{\text{2+}}\text{+ 2}{\text{e}}^{-}$

Changes in the electron configurations of the atom and magnesium cation are as follows:

$\text{Mg [2, 8, 2] }\stackrel{\text{donation of 2 electrons}}{\to }{\text{ Mg}}^{\text{2+}}\text{[2, 8]}$

Note that the magnesium cation has been recognized as a permanent neon electron configuration ($\text{Z = 10}$).

The sulfur atom forms a dianion.

The aluminum atom forms aluminum ions of the formula ${\text{Al}}^{\text{3+}}$. The number ‘3+’ means that the formed ion is a cation that was formed after the aluminum atom donated 3 electrons. The formation of aluminum ion can be described by the following equation:

$\text{Al → }{\text{Al}}^{\text{3+}}\text{+ 3}{\text{e}}^{-}$

After taking into account the electron configuration, it has the form:

$\text{Al [2, 8, 3] }\stackrel{\text{donation of 3 electrons}}{\to }{\text{ Al}}^{\text{3+}}\text{[2, 8]}$

The electron configuration in the aluminum cation is the same as in the neon atom ($\text{Z = 10}$).

• Ions are formed from atoms that have donated or accepted at least 1 electron.

• Ions having positive charge are cations; arise from atoms after donation at least 1 electron.

• Negatively charged ions are anions; arise from atoms that have accepted at least 1 electron.

• Cations are mainly formed from metal atoms, and anions – among others from the atoms of some non‑metals.